CODEWITHSUNDEEP
pythondjangodjango-orm
Chickenfresh
Chickenfresh

Reputation: 365

count the number of uses of each of the objects in another table

I have two models:

class FirstTable(models.Model):
    name = models.CharField(...)


class SecondTable(models.Model):
    examples = models.ManyToManyField(FirstTable)

I have a function which counts how many times FirstTable is used in SecondTable's examples field:

data = {}
for i in FirstTable.objects.all():
    data[i.name] = SecondTable.objects.filter(examples__exact=i).count()

but is it possible to get the same data with one request? (aggregate or annotate ways)

Upvotes: 0

Views: 31

Answers (1)

Sergey Pugach
Sergey Pugach

Reputation: 5669

You can do: 

from django.db.models import Count

FirstTable.objects.annotate(examples_count=Count('secondtable')).values('name', 'examples_count')

The output will be:

<QuerySet [{'name': 'Name1', 'examples_count': 3}, {'name': 'Name2', 'examples_count': 10}, ..., >

Upvotes: 1

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